Cathode catalysts for fuel cell development; a theoretical study based on band structure calculations for tungsten nitride and cobalt tungsten nitrides

Introduction Although platinum-containing catalysts are available as electrode catalysts for PEFCs, they are very expensive. Alternatives to Pt catalysts are being developed through ongoing experimental and theoretical studies. In recent years, with dramatic improvements in the performance of low-cost computers, several theoretical studies of the catalytic properties of electrode catalysts for PEFCs are have been undertaken. Lima et al. [1] have reported a correlation between the d-band center and the activities of the oxygen reduction reaction (ORR) on the surfaces of Au(111), Ag(111), Pd(111), Rh(111), Ir(111), and Ru(0001) on Pt monolayers, revealing a volcano-type dependence. The value of the d-band center is calculated relative to the Fermi level, and the value of the Fermi level is directly hidden. This quantification primarily reflects the d-band center, although we consider that the Fermi level is also an important factor in the activity of a cathode catalyst. Therefore, we have focused on the band structure rather than the DOS. Eberhart and MacLaren [2] have shown that band structures are related to the catalytic activities of carbides, whereas band structures are not relevant to the performances of catalysts as electrodes. In the present study, the band structures of tungsten nitrides and cobalt tungsten nitrides both before and after the adsorption of O2 were calculated, to examine the relationship between band structure and catalytic activity as a cathode. For adoption as a cathode catalyst, two of the requirements had to be met. The band structure of platinum is discussed for comparative purposes.